The objective of this research is to characterize quantitatively the rheological properties of cytoplasm in differentiated local regions of the following motile cells (or syncytia): the large amoebae, Chaos and amoeba; the large coenocytic alga, Nitella; the acellular slime mold, Physarum; and the large cilitate, Paramecium. The approach involves the displacement by a sensitive electromagnet of non-toxic iron microspheres. Yield point (pseudoplasticity), viscostiy, and both parallel and series elastic components will be measured by the force applied, the velocity of motion in a known magnetic field, and microsphere recoil dynamics. By recording experiments with polarized light and other optical techniques, and by varying the location and direction of microsphere displacement, coordinated measurements of optical and rheological anisotropy will be made. The proposed studies complement separately funded ultrastructural investigations of the cytoplasm of these same cells using both chemical fixation and cryopreservation-deep etch techniques. The ultimate aim is to measure the strength of association of cytoskeletal elements in cells in which the rheological properties of the cytoplasm are known to vary locally, and to correlate rheological information with both ultrastructural and biochemical information. The importance of the rheological approach is that it is the only direct means we have of measuring the interaction of biopolymers in the cell. Interpretation will be aided by calibration experiments on fluids of known rheological properties and model experiments on extracts and gels of cytoskeletal components under conditions known to modify their bulk behavior.